Multilayered fluorescent screens for scanning beam display systems

ABSTRACT

Fluorescent screens and display systems and devices based on such screens using at least one excitation optical beam to excite one or more fluorescent materials on a screen which emit light to form images. The fluorescent materials may include phosphor materials and non-phosphor materials such as quantum dots.

This application claims the benefits of U.S. Provisional Application No.60/800,870 entitled “Display Systems Using Fluorescent Screens IncludingFluorescent Screens With Prismatic Layer” and filed May 15, 2006, andPCT Patent Application No. PCT/US2006/11757 entitled “Display SystemsHaving Screens With Optical Fluorescent Materials” and filed Mar. 31,2006, the entire disclosures of which are incorporated by reference aspart of the specification of this application.

BACKGROUND

This application relates to display systems that use screens withfluorescent materials to emit colored light under optical excitation,such as laser-based image and video displays and screen designs for suchdisplays.

Many image and video displays are designed to directly produce colorimages in different colors, such as red, green and blue and then projectthe color images on a screen. Such systems are often referred to as“projection displays” where the screen is simply a surface to make thecolor images visible to a viewer. Such projection displays may use whitelight sources where white beams are filtered and modulated to produceimages in red, green and blue colors. Alternatively, three light sourcesin red, green and blue may be used to directly produce three beams inred, green and blue colors and the three beams are modulated to produceimages in red, green and blue. Examples of such projection displaysinclude digital light processing (DLP) displays, liquid crystal onsilicon (LCoS) displays, and grating light valve (GLV) displays.Notably, GLV displays use three grating light valves to modulate red,green and blue laser beams, respectively, and use a beam scanner toproduce the color images on a screen. Another example of laser-basedprojection displays is described in U.S. Pat. No. 5,920,361 entitled“Methods and apparatus for image projection.” Projection displays useoptical lens systems to image and project the color images on thescreen.

Some other image and video displays use a “direct” configuration wherethe screen itself includes light-producing color pixels to directly formcolor images in the screen. Such direct displays eliminate the opticallens systems for projecting the images and therefore can be maderelatively smaller than projection displays with the same screen sizes.Examples of direct display systems include plasma displays, liquidcrystal displays (LCDs), light-emitting-diode (LED) displays (e.g.,organic LED displays), and field-emission displays (FEDs). Each colorpixel in such direct displays includes three adjacent color pixels whichproduce light in red, green and blue, respectively, by either directlyemit colored light as in LED displays and FEDs or by filtering whitelight such as the LCDs.

These and other displays are replacing cathode-ray tube (CRT) displayswhich dominated the display markets for decades since its inception. CRTdisplays use scanning electron beams in a vacuum tube to excite colorphosphors in red, green and blue colors on the screen to emit coloredlight to produce color images. Although CRT displays can produce vividcolors and bright images with high resolutions, the use of cathode-raytubes places severe technical limitations on the CRT displays and leadsto dramatic decline in demand for CRT displays in recent years.

SUMMARY

The specification of this application describes, among others,fluorescent screens, and display systems and devices based on suchscreens using at least one excitation optical beam to excite one or morefluorescent materials on a screen which emit light to form images. Thefluorescent materials may include phosphor materials and non-phosphormaterials such as quantum dots.

In one example, a display screen includes parallel screen layers whichare engaged to form a planar stack and include a fluorescent layerabsorbing excitation light at an excitation wavelength to emit visiblelight at a different visible wavelength, and a prismatic layer includinga plurality of prism elements which receive and couple the excitationlight to the fluorescent layer.

In another example, a display screen includes screen layers which areengaged to form a planar stack and include a fluorescent layer includingparallel fluorescent stripes and absorbing excitation light at anexcitation wavelength to emit visible light at a different and visiblewavelength. The screen layers also include parallel stripe dividers eachlocated between two adjacent fluorescent stripes. Each strip dividerincludes side walls that are reflective and opaque to the emittedvisible light to optically isolate two adjacent fluorescent stripes. Adielectric layer is included to be in contact with the stripe dividersand spaced from the fluorescent layer to define a gap between thedielectric layer and each fluorescent stripe.

In another example, a display screen includes a screen substrate, and afluorescent layer formed over the screen substrate to include parallelfluorescent stripes which absorb excitation light to emit visible light.The excitation light and the visible light are at different wavelengths.The display screen also include parallel stripe dividers each locatedbetween two adjacent fluorescent stripes, and a dichroic layer formedover the screen substrate to receive the excitation light. The dichroiclayer transmits the excitation light and reflects the visible light.

In another example, a display screen includes a fluorescent layer whichincludes parallel fluorescent stripes that absorb excitation light toemit visible light. The excitation light and the visible light are atdifferent wavelengths. An entrance layer is formed on a first side ofthe fluorescent layer to receive the excitation light and to direct theexcitation light to the fluorescent layer. A filter layer is also formeda second side of the fluorescent layer opposing the first side. Thisfilter layer is formed of a material that transmits the visible lightwith an attenuation uniform over a spectral range of the visible light.

In yet another example, a display screen includes a fluorescent layerthat absorbs excitation light to emit visible light; and a first layeron a first side of the fluorescent layer operable to transmit theexcitation light and to reflect the visible light. The first layerincludes a prismatic layer which comprises prism elements.

In yet another example, a display screen includes a fluorescent layerthat absorbs excitation light to emit white light, and an array of colorfilters adjacent to the fluorescent layer to receive the emitted whitelight and to filter the white light to transmit colored light. Eachcolor filter transmits a designated color and absorbs light of othercolors. Each designated color for one color filter is different from adesignated color transmitted by a neighboring color filter.

In yet another example, a display screen includes a first dielectriclayer that transmits excitation light at an excitation wavelength; afluorescent layer having parallel fluorescent stripes and absorbing theexcitation light to emit visible light at a different and visiblewavelength; and a second dielectric layer spaced from the fluorescentstripes by an air gap. The second dielectric layer at least partiallytransmits the visible light. The fluorescent layer is positioned betweenthe first and second dielectric layers.

These and other examples and implementations are described in detail inthe drawings, the detailed description, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example scanning laser display system having afluorescent screen made of laser-excitable fluorescent materials (e.g.,phosphors) emitting colored lights under excitation of a scanning laserbeam that carries the image information to be displayed.

FIGS. 2A and 2B show one example screen structure and the structure ofcolor pixels on the screen in FIG. 1.

FIG. 3 shows an example implementation of the laser module in FIG. 1having multiple lasers that direct multiple laser beams on the screen.

FIG. 4 illustrates an example screen having a fluorescent stripe layerwith fluorescent stripes for emitting red, green and blue colors underoptical excitation of the scanning excitation light.

FIG. 5 shows an example fluorescent layer with fluorescent stripesformed on a supporting substrate.

FIG. 6 shows an example of a fluorescent screen with two dichroiclayers.

FIGS. 7A and 7B illustrate two screen examples based on the screendesign in FIG. 6.

FIG. 8 shows a fluorescent screen design with a contrast enhancementlayer.

FIG. 9 shows a fluorescent screen design with a contrast enhancementmaterial composition in each fluorescent stripe.

FIG. 10 illustrates an example of a fluorescent screen design that has acontiguous and uniform layer of mixed phosphors that emits white light.

FIGS. 11 and 12 show a fluorescent screen design with a Fresnel lenslayer to direct scanning input excitation light to the fluorescentscreen.

FIG. 13 shows a prismatic layer as an entrance layer for scanningexcitation light in a fluorescent screen.

FIG. 13A illustrates an operation of the prismatic layer in FIG. 13.

FIG. 14 shows a high-index layer as an entrance layer for scanningexcitation light in a fluorescent screen.

FIGS. 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 and 25 show various screendesigns.

FIG. 26 shows an implementation of a low-index dielectric layer such asan air gap on the viewer side of the fluorescent layer in a fluorescentscreen to improve the image quality of the fluorescent screen.

DETAILED DESCRIPTION

This application describes scanning beam display systems that usescreens with fluorescent materials to emit light under opticalexcitation to produce images, including laser video display systems.Various examples of screen designs with fluorescent materials aredescribed. Screens with phosphor materials under excitation of one ormore scanning excitation laser beams are described in detail and areused as specific implementation examples of optically excitedfluorescent materials in various system and device examples in thisapplication.

In one implementation, for example, three different color phosphors thatare optically excitable by the laser beam to respectively produce lightin red, green, and blue colors suitable for forming color images may beformed on the screen as pixel dots or repetitive red, green and bluephosphor stripes in parallel. Various examples described in thisapplication use screens with parallel color phosphor stripes foremitting light in red, green, and blue to illustrate various features ofthe laser-based displays.

Phosphor materials are one type of fluorescent materials. Variousdescribed systems, devices and features in the examples that usephosphors as the fluorescent materials are applicable to displays withscreens made of other optically excitable, light-emitting, non-phosphorfluorescent materials. For example, quantum dot materials emit lightunder proper optical excitation and thus can be used as the fluorescentmaterials for systems and devices in this application. Morespecifically, semiconductor compounds such as, among others, CdSe andPbS, can be fabricated in form of particles with a diameter on the orderof the exciton Bohr radius of the compounds as quantum dot materials toemit light. To produce light of different colors, different quantum dotmaterials with different energy band gap structures may be used to emitdifferent colors under the same excitation light. Some quantum dots arebetween 2 and 10 nanometers in size and include approximately tens ofatoms such between 10 to 50 atoms. Quantum dots may be dispersed andmixed in various materials to form liquid solutions, powders, jelly-likematrix materials and solids (e.g., solid solutions). Quantum dot filmsor film stripes may be formed on a substrate as a screen for a system ordevice in this application. In one implementation, for example, threedifferent quantum dot materials can be designed and engineered to beoptically excited by the scanning laser beam as the optical pump toproduce light in red, green, and blue colors suitable for forming colorimages. Such quantum dots may be formed on the screen as pixel dotsarranged in parallel lines (e.g., repetitive sequential red pixel dotline, green pixel dot line and blue pixel dot line).

Examples of scanning beam display systems described here use at leastone scanning laser beam to excite color light-emitting materialsdeposited on a screen to produce color images. The scanning laser beamis modulated to carry images in red, green and blue colors or in othervisible colors and is controlled in such a way that the laser beamexcites the color light-emitting materials in red, green and blue colorswith images in red, green and blue colors, respectively. Hence, thescanning laser beam carries the images but does not directly produce thevisible light seen by a viewer. Instead, the color light-emittingfluorescent materials on the screen absorb the energy of the scanninglaser beam and emit visible light in red, green and blue or other colorsto generate actual color images seen by the viewer.

Laser excitation of the fluorescent materials using one or more laserbeams with energy sufficient to cause the fluorescent materials to emitlight or to luminesce is one of various forms of optical excitation. Inother implementations, the optical excitation may be generated by anon-laser light source that is sufficiently energetic to excite thefluorescent materials used in the screen. Examples of non-laserexcitation light sources include various light-emitting diodes (LEDs),light lamps and other light sources that produce light at a wavelengthor a spectral band to excite a fluorescent material that converts thelight of a higher energy into light of lower energy in the visiblerange. The excitation optical beam that excites a fluorescent materialon the screen can be at a frequency or in a spectral range that ishigher in frequency than the frequency of the emitted visible light bythe fluorescent material. Accordingly, the excitation optical beam maybe in the violet spectral range and the ultra violet (UV) spectralrange, e.g., wavelengths under 420 nm. In the examples described below,UV light or a UV laser beam is used as an example of the excitationlight for a phosphor material or other fluorescent material and may belight at other wavelength.

FIG. 1 illustrates an example of a laser-based display system using ascreen having color phosphor stripes. Alternatively, color phosphor dotsmay also be used to define the image pixels on the screen. The systemincludes a laser module 110 to produce and project at least one scanninglaser beam 120 onto a screen 101. The screen 101 has parallel colorphosphor stripes in the vertical direction where red phosphor absorbsthe laser light to emit light in red, green phosphor absorbs the laserlight to emit light in green and blue phosphor absorbs the laser lightto emit light in blue. Adjacent three color phosphor stripes are inthree different colors. One particular spatial color sequence of thestripes is shown in FIG. 1 as red, green and blue. Other color sequencesmay also be used. The laser beam 120 is at the wavelength within theoptical absorption bandwidth of the color phosphors and is usually at awavelength shorter than the visible blue and the green and red colorsfor the color images. As an example, the color phosphors may bephosphors that absorb UV light in the spectral range from about 380 nmto about 420 nm to produce desired red, green and blue light. The lasermodule 110 can include one or more lasers such as UV diode lasers toproduce the beam 120, a beam scanning mechanism to scan the beam 120horizontally and vertically to render one image frame at a time on thescreen 101, and a signal modulation mechanism to modulate the beam 120to carry the information for image channels for red, green and bluecolors. Such display systems may be configured as rear projectionsystems where the viewer and the laser module 110 are on the oppositesides of the screen 101. Alternatively, such display systems may beconfigured as front projection systems where the viewer and laser module110 are on the same side of the screen 101.

FIG. 2A shows an exemplary design of the screen 101 in FIG. 1. Thescreen 101 may include a rear substrate 201 which is transparent to thescanning laser beam 120 and faces the laser module 110 to receive thescanning laser beam 120. A second front substrate 202, is fixed relativeto the rear substrate 201 and faces the viewer in a rear projectionconfiguration. A color phosphor stripe layer 203 is placed between thesubstrates 201 and 202 and includes phosphor stripes. The color phosphorstripes for emitting red, green and blue colors are represented by “R”,“G” and “B,” respectively. The front substrate 202 is transparent to thered, green and blue colors emitted by the phosphor stripes. Thesubstrates 201 and 202 may be made of various materials, including glassor plastic panels. Each color pixel includes portions of three adjacentcolor phosphor stripes in the horizontal direction and its verticaldimension is defined by the beam spread of the laser beam 120 in thevertical direction. As such, each color pixel includes three subpixelsof three different colors (e.g., the red, green and blue). The lasermodule 110 scans the laser beam 120 one horizontal line at a time, e.g.,from left to right and from top to bottom to fill the screen 101. Thelaser module 110 is fixed in position relative to the screen 101 so thatthe scanning of the beam 120 can be controlled in a predetermined mannerto ensure proper alignment between the laser beam 120 and each pixelposition on the screen 101.

In FIG. 2A, the scanning laser beam 120 is directed at the greenphosphor stripe within a pixel to produce green light for that pixel.FIG. 2B further shows the operation of the screen 101 in a view alongthe direction B-B perpendicular to the surface of the screen 101. Sinceeach color stripe is longitudinal in shape, the cross section of thebeam 120 may be shaped to be elongated along the direction of the stripeto maximize the fill factor of the beam within each color stripe for apixel. This may be achieved by using a beam shaping optical element inthe laser module 110. A laser source that is used to produce a scanninglaser beam that excites a phosphor material on the screen may be asingle mode laser or a multimode laser. The laser may also be a singlemode along the direction perpendicular to the elongated directionphosphor stripes to have a small beam spread that is confined by thewidth of each phosphor stripe. Along the elongated direction of thephosphor stripes, this laser beam may have multiple modes to spread overa larger area than the beam spread in the direction across the phosphorstripe. This use of a laser beam with a single mode in one direction tohave a small beam footprint on the screen and multiple modes in theperpendicular direction to have a larger footprint on the screen allowsthe beam to be shaped to fit the elongated color subpixel on the screenand to provide sufficient laser power in the beam via the multimodes toensure sufficient brightness of the screen.

Each of the fluorescent stripes in the fluorescent screen 101 in variousexamples described in this application is a fluorescent stripe thatemits a designated color under optical excitation and can be afluorescent stripe formed of a particular fluorescent material thatemits the designed color as shown in the example in FIG. 2A.Alternatively, a fluorescent stripe can be constructed by a combinationof a stripe color filter over a contiguous and uniform white fluorescentlayer that is made of mixed phosphors that emit white light underoptical excitation of the excitation light 120. Hence, a filter layer ofcolor filters, such as stripes of red-transmitting, green-transmittingand blue-transmitting filters, is placed on the viewer side of the mixedphosphor layer to filter the white light and to produce colored outputlight. The details of the construction of the fluorescent stripes aredescribed in a later section of this specification with reference toFIG. 10. In this context, a fluorescent layer has a composite structurewith a filter layer and a contiguous fluorescent layer that emits whitelight.

Referring now to FIG. 3, an example implementation of the laser module110 in FIG. 1 is illustrated. A laser array 310 with multiple lasers isused to generate multiple laser beams 312 to simultaneously scan thescreen 101 for enhanced display brightness. A signal modulationcontroller 320 is provided to control and modulate the lasers in thelaser array 310 so that the laser beams 312 are modulated to carry theimage to be displayed on the screen 101. The signal modulationcontroller 320 can include a digital image processor that generatesdigital image signals for the three different color channels and laserdriver circuits that produce laser control signals carrying the digitalimage signals. The laser control signals are then applied to modulatethe lasers, e.g., the currents for laser diodes, in the laser array 310.

The beam scanning can be achieved by using a scanning mirror 340 such asa galvo mirror for the vertical scanning and a multi-facet polygonscanner 350 for the horizontal scanning. A scan lens 360 can be used toproject the scanning beams form the polygon scanner 350 onto the screen101. The scan lens 360 is designed to image each laser in the laserarray 310 onto the screen 101. Each of the different reflective facetsof the polygon scanner 350 simultaneously scans N horizontal lines whereN is the number of lasers. In the illustrated example, the laser beamsare first directed to the galvo mirror 340 and then from the galvomirror 340 to the polygon scanner 350. The output scanning beams 120 arethen projected onto the screen 101. A relay optics module 330 is placedin the optical path of the laser beams 312 to modify the spatialproperty of the laser beams 312 and to produce a closely packed bundleof beams 332 for scanning by the galvo mirror 340 and the polygonscanner 350 as the scanning beams 120 projected onto the screen 101 toexcite the phosphors and to generate the images by colored light emittedby the phosphors.

The laser beams 120 are scanned spatially across the screen 101 to hitdifferent color pixels at different times. Accordingly, each of themodulated beams 120 carries the image signals for the red, green andblue colors for each pixel at different times and for different pixelsat different times. Hence, the beams 120 are coded with imageinformation for different pixels at different times by the signalmodulation controller 320. The beam scanning thus maps the time-domaincoded image signals in the beams 120 onto the spatial pixels on thescreen 101. For example, the modulated laser beams 120 can have eachcolor pixel time equally divided into three sequential time slots forthe three color subpixels for the three different color channels. Themodulation of the beams 120 may use pulse modulation techniques toproduce desired grey scales in each color, a proper color combination ineach pixel, and desired image brightness.

In one implementation, the multiple beams 120 are directed onto thescreen 101 at different and adjacent vertical positions with twoadjacent beams being spaced from each other on the screen 101 by onehorizontal line of the screen 101 along the vertical direction. For agiven position of the galvo mirror 340 and a given position of thepolygon scanner 350, the beams 120 may not be aligned with each otheralong the vertical direction on the screen 101 and may be at differentpositions on the screen 101 along the horizontal direction. The beams120 can only cover one portion of the screen 101. At a fixed angularposition of the galvo mirror 340, the spinning of the polygon scanner350 causes the beams 120 from N lasers in the laser array 310 to scanone screen segment of N adjacent horizontal lines on the screen 101. Atend of each horizontal scan over one screen segment, the galvo mirror340 is adjusted to a different fixed angular position so that thevertical positions of all N beams 120 are adjusted to scan the nextadjacent screen segment of N horizontal lines. This process iteratesuntil the entire screen 101 is scanned to produce a full screen display.

The stripe design in FIG. 2B for the fluorescent screen 101 in FIGS. 1and 3 can be implemented in various configurations. FIG. 2A shows oneexample which places the fluorescent layer 203 such as a color phosphorstripe layer between two substrates 201 and 202. In a rear projectionsystem, it is desirable that the screen 101 couple as much light aspossible in the incident scanning excitation beam 120 into thefluorescent layer with while maximizing the amount of the emitted lightfrom the fluorescent layer that is directed towards the viewer side. Anumber of screen mechanisms can be implemented, either individually orin combination, in the screen 101 to enhance the screen performance,including efficient collection of the excitation light, maximization offluorescent light directed towards the viewer side, enhancement of thescreen contrast and reduction the screen glare. The structure andmaterials of the screen 101 can be designed and selected to meetconstraints on cost and other requirements for specific applications.

FIG. 4 illustrates an example screen 101 having a fluorescent stripelayer with fluorescent stripes for emitting red, green and blue colorsunder optical excitation of the scanning excitation light. A number ofscreen features are illustrated as examples and can be selectivelyimplemented in specific screens. Hence, a particular fluorescent screenhaving only some of the features illustrated in FIG. 4 may be sufficientfor a particular display application.

The fluorescent screen 101 in FIG. 4 includes at least one substratelayer 424 to provide a rigid structural support for various screencomponents including a fluorescent layer 400. This substrate layer 424can be a thin substrate or a rigid sheet. When placed on the viewer sideof the fluorescent layer 400 as illustrated in FIG. 4, the substratelayer 424 can be made of a material transparent or partially transparentto the visible colored light emitted by the fluorescent stripes 401,402, 403. A partial transparent material can have a uniform attenuationto the visible light including the three colors emitted by thefluorescent stripes to operate like an optical neutral density filter.The substrate layer 424 can be made of a plastic material, a glassmaterial, or other suitable dielectric material. For example, thesubstrate layer 424 may be made of an acrylic rigid sheet. The thicknessof the substrate layer 424 may be a few millimeters in some designs. Inaddition, the substrate layer 424 may be made reflective and opaque tothe excitation light of the excitation beam 120 to block the excitationlight from reaching the viewer and to recycle the unabsorbed excitationlight back to the fluorescent layer 400.

The substrate layer 424 can also be located on the other side of thefluorescent layer 400. Because the excitation beam 120 must transmitthrough the substrate layer 424 to enter the fluorescent layer 400, thematerial for the substrate layer 424 should be transparent to theexcitation light of the excitation beam 120. In addition, the substratelayer 424 in this configuration may also be reflective to the visiblelight emitted by the fluorescent layer 400 to direct any emitted visiblelight coming from the fluorescent layer 400 towards the viewer side toimprove the brightness of the displayed images.

The fluorescent layer 400 includes parallel fluorescent stripes withrepetitive color patterns such as red, green and blue phosphor stripes.The fluorescent stripes are perpendicular to the horizontal scandirection of the scanning excitation beam 120 shown in FIG. 1. Asillustrated in FIG. 4 and in FIG. 2B, each display pixel on the screenincludes three subpixels which are portions of adjacent red, green andblue stripes 401, 402 and 402. The dimension of each subpixel along thehorizontal direction is defined by the width of each stripe and thedimension along the vertical direction is defined by the beam widthalong the vertical direction. A stripe divider 404, which can beoptically reflective and opaque, or optically absorbent, may be formedbetween any two adjacent fluorescent stripes to minimize or reduce thecross talk between two adjacent subpixels. As a result, the smearing ata boundary between two adjacent subpixels within one color pixel andbetween two adjacent color pixels can be reduced, and the resolution andcontrast of the screen can be improved. The sidewalls of each stripedivider 404 can be made optically reflective to improve the brightnessof each subpixel and the efficiency of the screen.

The above basic structure of the substrate layer 424 and the fluorescentlayer 400 can be used as a building block to add one or more screenelements to enhance various properties and the performance of thescreen. The fluorescent layer 400 is an optically active layer in thecontext that the excitation light at the excitation wavelength isabsorbed by the fluorescent materials and is converted into visiblefluorescent light of different colors for displaying the images to theviewer. In this regard, the fluorescent layer 400 is also the divisionbetween the “excitation side” and the “viewer side” of the screen wherethe optical properties of the two sides are designed very differently inorder to achieve desired optical effects in each of two sides to enhancethe screen performance. Examples of such optical effects include,enhancing coupling of the excitation beam 120 into the fluorescentlayer, recycling reflected and scattered excitation light that is notabsorbed by the fluorescent layer 400 back into the fluorescent layer400, maximizing the amount of the emitted visible light from thefluorescent layer 400 towards the viewer side of the screen, reducingscreen glare to the viewer caused by reflection of the ambient light,blocking the excitation light from existing the screen towards theviewer, and enhancing the contrast of the screen. Various screenelements can be configured to achieve one or more of these opticaleffects. Several examples of such screen elements are illustrated inFIG. 4.

Referring to FIG. 4, at the entry side of the screen facing theexcitation beam 120, an entrance layer 411 can be provided to couple theexcitation beam 120 into the screen 101. A Fresnel lens layer can beused as this entrance layer 411 to control the incidence direction ofthe scanning excitation beam 120. A prismatic layer or a high-indexdielectric layer can also be used as part of the entrance layer 411 torecycle light back into the screen including the excitation light andthe emitted visible light by the fluorescent layer. To improve thebrightness of the screen to the viewer, a first dichroic layer 412 (D1)can be placed in the path of the excitation beam 120 upstream from thefluorescent layer 400 to transmit light at the wavelength of theexcitation beam 120 and to reflect visible light emitted by thefluorescent layer 400. The first dichroic layer 412 can reduce theoptical loss of the fluorescent light and thus enhances the screenbrightness. On the viewer side of the fluorescent layer 400, a seconddichroic layer 421 (D2) can be provided to transmit the visible lightemitted by the fluorescent layer 400 and to reflect light at thewavelength of the excitation beam 120. Hence, the second dichroic layer421 can recycle the excitation light that passes through the fluorescentlayer 400 back to the fluorescent layer 400 and thus increases theutilization efficiency of the excitation light and the screenbrightness.

On the viewer side of the fluorescent layer 400, a contrast enhancementlayer 422 can be included to improve the screen contrast. The contrastenhancement layer 422 can include color-selective absorbing stripes thatspatially correspond to and align with fluorescent stripes in thefluorescent layer 400 along the direction perpendicular to the screenlayers. The color-selective absorbing stripes therefore transmit lightin respective colors of the fluorescent stripes and absorb light incolors of other fluorescent stripes, respectively. Alternatively, thecontrast enhancement layer 422 can be an optical neutral density filterlayer that uniformly attenuates the visible light to reduce the glare ofthe screen due to the reflection of the ambient light. This neutraldensity filtering function may also be implemented in one or more otherlayers on the viewer side of the fluorescent layer 400, including thesubstrate layer 424.

In addition, the screen can include a screen gain layer 423 on theviewer side of the fluorescent layer 400 to optically enhance thebrightness and viewing angle of the screen. The gain layer 423 mayinclude a lenticular layer with lens elements, a diffractive optic layerof diffractive elements, a holographic layer with holographic elements,or a combination of these and other structures. The spatial sequence ofthe layers 423, 422 and 421 on the viewer side of the fluorescent layer400 may be different from what is shown in FIG. 4.

Furthermore, an excitation blocking layer 425 can be placed on theviewer side of the fluorescent layer 400 to block any excitation lightfrom exiting the screen to the viewer side. This layer can beimplemented by a material that transmits the visible light and absorbsthe excitation light. For example, a polyester based color filter can beused as this layer to block the excitation light which may be radiationfrom 400-415 nm. In some implementations, this blocking filter may havetransmission below 410 nm less than 0.01%, while having greater than 50%transmission above 430 nm. The neutral density filtering function canalso be incorporated in this layer, e.g., having a uniform attenuationto the visible light between 430 nm and 670 nm. This blocking functioncan be incorporated into the substrate layer 424.

FIG. 5 shows an example fluorescent layer 400 formed on a supportingsubstrate 501. The fluorescent layer 400 has fluorescent stripes whereadjacent three stripes are 401, 402, 403 for emitting red, green andblue colors, respectively. The supporting substrate 501 includesparallel raised lands 502 as stripe dividers to divide the surface intoparallel channels in which the fluorescent materials are placed to formthe fluorescent stripes 401, 402, 403, etc. The sidewalls of the raisedlands 502 physically separate the different fluorescent stripes and canbe made optically reflective and opaque to block crosstalk or colormixing between two adjacent fluorescent stripes that emit two differentcolors, respectively. The reflective sidewalls of the raised lands 502prevent loss of light emitted in each fluorescent stripe. In addition,the parallel channels formed between the raided lands 502 can be used tocontrol the volume of the fluorescent material deposited during theformation of the fluorescent layer.

FIG. 6 shows an example of a fluorescent screen with two dichroic layers412 and 421. A fluorescent layer 610 includes different fluorescent orphosphor layers for different colors are formed at different layers anddo not overlap with one another. As illustrated, each layer includespatterned phosphor regions of the same phosphor for one color andnon-phosphor regions 620 with a filler material that is transparent. Thedividers 404 for reducing color crosstalk may be physically printed withcolor phosphors, or contained in separate layers. The multi-layerstructure of the fluorescent layer 610 may be implemented in differentconfigurations. For example, a host substrate can be used to supportdifferent phosphors where non-overlapping phosphor patterns are coatedon either side of the substrate. This design of the phosphor layersallows different phosphor layers to be individually fabricated andlaminated together by, e.g., using a suitable optical adhesive or anoptical pressure-sensitive film. A substrate or rigid sheet 630 islocated on the excitation side of the fluorescent layer 610 to supportthe various layers of the screen and can be made from, e.g., acrylic,rigid optical plastic material, a stretched membrane, and a glassmaterial. An anti-reflection (AR) layer 640 can be formed on the surfaceof the substrate 630 through which the excitation beam 120 enters thescreen.

Turning now specifically to the dichroic layers 412 and 421 in FIG. 4,the first dichroic layer D1 412 can prevent loss of light emitted fromthe fluorescent layer 400 towards the excitation side and reflect theemitted light towards the viewer side. The second dichroic layer 421(D2) is to transmit the visible light and to reflect light at thewavelength of the excitation laser light 120. This screen design withthe two dichroic layers 412 and 421 can effectively confine theexcitation light such as UV light within the fluorescent layer 400 sothat the unabsorbed excitation light, after passing through thefluorescent layer 400, is reflected back by the dichroic layer 421 (D2)to continue interacting with the fluorescent materials in thefluorescent layer 400 to improve the utility efficiency of theexcitation light. In addition, the visible light emitted by thefluorescent layer 400, which originally tends to be in all directions,is directed by the dichroic layer 412 (D1) towards the viewer side ofthe screen to be viewed by a viewer without leaking to the excitationside of the screen. Accordingly, the overall utility efficiency of theemitted light and the brightness of the screen can be enhanced.

FIGS. 7A and 7B illustrate two screen examples based on the above screendesign. A substrate 701 is provided to support the dichroic layers 412,421 and the fluorescent layer 400. FIG. 7A shows an example where thesubstrate 701 is on the side of the dichroic layer 421 so that theemitted light exits the screen through the substrate 701. FIG. 7B showsan example where the substrate 701 is on the side of the dichroic layer412 and the incident excitation beam 120 enters the screen through thesubstrate 701. In one example, the excitation beam 120 can be UV laserlight around 405 nm. The D1 layer 412 reflects visible light with awavelength greater than 430 nm and transmits UV light with a wavelengthshorter than 415 nm or 400 nm. In this example, the D2 layer 421reflects UV light with a wavelength shorter than 415 nm or even lessthan 400 nm and transmits visible light with a wavelength greater than430 nm. Anti-reflection (AR) coatings may be used to further enhance theefficiency of the screen.

The configuration in FIG. 7A provides better transmission properties forthe excitation light such as UV light, a minimum back reflection towardsthe excitation side, and allows the substrate 701 to act as a shieldfrom the user interface side. The configuration in FIG. 7B allows thesubstrate 701 to be treated to form an optical diffractive element andother optical features in the entrance layer 411 to improve the couplingand recycling of the excitation light. A hard protective surface, e.g.,a lacquer layer or capsulation layer may be formed on the viewer or userside of the screen to protect the screen from handling and environmentalconditions.

TABLE 1 CONSTRUC- TION 1st 5th 6^(th) TYPE Layer 2nd layer 3^(rd) layer4^(th) Layer Layer Layer Surface D1 Phosphor D2 S AR Incident Surface LD1 Phosphor D2 S AR Incident Substrate AR Substrate D1 Phosphor D2 LIncident Substrate AR Substrate D1 Phosphor D2 AR Incident

TABLE 1 shows four examples of 6-layer screens where the layers arelabeled 1 through 6 in the spatial order from the excitation side to theviewer side of the screen. One or more phosphors are used to form thefluorescent layer and a capsulation layer such as a lacquer layer (L) isused to protect the overall screen structure from handling andenvironmental conditions. The substrate may be made of a plastic orglass material and, when located on the viewer side of the fluorescentlayer, is capable of transmitting light in the spectral range of thevisible light, e.g., 400-800 nm. Anti-reflective (AR) coating layers arealso included in these examples.

Each of the above dichroic layers D1 (412) and D2 (421) may beimplemented in various configurations. For large format displays, such adichroic layer may be made of relatively inexpensive materials and berelatively easy to manufacture. Multiple dielectric layers can bedesigned to construct various wavelength-selective optical filters bycontrolling the refractive indices and the physical thickness values ofthe layers. For example, multiple layers of alternating high and lowindex dielectric layers may be designed to achieve desiredwavelength-selective reflection and transmission spectra. Multiplesheets of films with different refractive indices may be laminated orfused together to construct a composite sheet as the D1 or D2 dichroiclayer. In some implementations, multiple layers of two differentmaterials with different indices may be used to form a composite filmstack as D1 or D2 by placing the two materials in an alternating manner.In other implementations, three or more different materials withdifferent indices may be stacked together to form the composite filmstack as D1 or D2. Such a composite sheet for the D1 layer isessentially an optical interference reflector that transmits theexcitation light (e.g., UV light) and reflects the colored visiblelight. The materials for the composite sheets may be organic materials,inorganic materials or a combination of organic and inorganic materialsthat can be rigid or flexible.

A flexible multi-layer composite sheet may be formed from polymeric,non-polymeric materials, or polymeric and non-polymeric materials.Exemplary films including a polymeric and non-polymeric material aredisclosed in U.S. Pat. No. 6,010,751 entitled “Method for forming amulticolor interference coating” and U.S. Pat. No. 6,172,810 entitled“Retroreflective articles having polymer multilayer reflectivecoatings,” which are incorporated by reference in their entirety as partof the specification of this application. An all-polymer constructionfor a composite sheet can offer manufacturing and cost benefits. Hightemperature polymers with high optical transmission and large indexdifferentials can be used to construct the interference filter that isenvironmentally stable, thin and flexible. Coextruded multilayerinterference filters as disclosed in U.S. Pat. No. 6,531,230 entitled“Color shifting film” can be used to provide precise wavelengthselection and can be made as a filter film in a large area at arelatively low cost. The entire disclosure of U.S. Pat. No. 6,531,230 isincorporated by reference as part of the specification of thisapplication. The use of polymer pairs having high index differentialsallows the construction of thin, highly reflective mirrors that arefreestanding without a substrate and can be easily processed forconstructing large screens. Such a composite sheet is functionally apiece of a multi-layer optical film (MOF) which can be, e.g., a stack ofalternating layers of PET and co-PMMA to exhibit a normal-incidencereflection band suitable for screen applications. As an example, anenhanced specular reflector (ESR) made out of a multilayerpolyester-based film from 3M Corporation may be configured to producethe desired dichroic reflection and transmission bands for the presentapplication. Examples for various features of multi-layer films aredescribed in U.S. Pat. No. 5,976,424 entitled “Method for makingmultilayer optical films having thin optical layers,” U.S. Pat. No.5,080,467 entitled “Biphenyl derivatives for photostabilization inpulsed optical darkening apparatus and method” and U.S. Pat. No.6,905,220 entitled “Backlight system with multilayer optical filmreflector,” all of which are incorporated by reference as part of thespecification of this application.

The stripe dividers shown in FIGS. 4, 5 and 6 provide physicalseparation and optical isolation between different subpixels and canenhance the image contrast by reducing crosstalk between differentsubpixels and different pixels. Such crosstalks are caused by theinternal structure of the screen. Various external factors can alsoadversely affect the image contrast and other performance parameters ofthe screens. For example, a portion of the ambient light can bereflected off the screen and enter a viewer's eyes along with thedisplayed image formed by the emitted fluorescent light. This reflectionof the ambient light towards the viewer generates a glare on the screento the viewer and can reduce the contrast of the image perceived by theviewer. A contrast enhancement layer, such as the layer 422 in FIG. 4,can be used to reduce the glare.

FIG. 8 shows one example of a screen 800 that uses a contrastenhancement layer 810 on the viewer side of the fluorescent layer 820.The fluorescent layer 820 such as a phosphor layer includes parallelphosphor stripes. Accordingly, the contrast enhancement layer 810 alsoincludes matching parallel stripes made of different materials. For ared phosphor stripe 821 that emits red light in response to excitationby the excitation light (e.g., UV or violet light), the matching stripe811 in the contrast enhancement layer 810 is made of a “red” materialthat transmits in a red spectral band covering the red light emitted bythe red phosphor stripe 821 and absorbs or otherwise blocks othervisible light including the green and blue light. Similarly, for a greenphosphor stripe that emits green light in response to excitation by UVlight, the matching stripe in the contrast enhancement layer 810 is madeof a “green” material that transmits in a green spectral band coveringthe green light emitted by the green phosphor and absorbs or otherwiseblocks other visible light including the red and blue light. For a bluephosphor stripe that emits blue light in response to excitation by UVlight, the matching stripe in the contrast enhancement layer 810 is madeof a “blue” material that transmits in a blue spectral band covering theblue light emitted by the blue phosphor and absorbs or otherwise blocksother visible light including the green and red light. These matchingparallel stripes in the contrast enhancement layer 810 are labeled as“R,” “G” and “B,” respectively.

In this example, the contrast enhancement layer 810 includes differentstripe filtering regions that spatially align with and match respectivefluorescent regions along the direction perpendicular to the screen.Each filtering region transmits light of a color that is emitted by acorresponding matching fluorescent region and blocks light of othercolors. Different filtering regions in the layer 810 may be made ofmaterials that absorb light of other colors different from the colorsemitted by the respective matching fluorescent regions. Examples ofsuitable materials include dye-based colorants and pigment-basedcolorants. In addition, each filtering region in the contrastenhancement layer 810 can be a multi-layer structure that effectuates aband-pass interference filter with a desired transmission band. Variousdesigns and techniques may be used for designing and constructing suchfilters. U.S. Pat. No. 5,587,818 entitled “Three color LCD with a blackmatrix and red and/or blue filters on one substrate and with greenfilters and red and/or blue filters on the opposite substrate,” and U.S.Pat. No. 5,684,552 entitled “Color liquid crystal display having a colorfilter composed of multilayer thin films” describe examples of red,green and blue filters that may be used in the layer 810 in the screen800 in FIG. 8.

In operation, the excitation light 120 (e.g., UV light) enters thephosphor layer 820 to excite different phosphors to emit visible lightof different colors. The emitted visible light transmits through thecontrast enhancement layer 810 to reach the viewer. The ambient light801 incident to the screen 800 enters the contrast enhancement layer 810and a portion of the incident ambient light 801 is reflected towards theviewer by passing through the contrast enhancement layer 810 for thesecond time. Therefore, the total optical output 802 towards the viewerincludes image-carrying colored visible light emitted by the phosphorlayer 820 and the reflected ambient light. This reflected ambient lightdoes not carry image and thus tends to wash out the image produced atthe phosphor layer 820. Because this reflected ambient light towards theviewer has passed the contrast enhancement layer 810 twice and thus hasbeen filtered and attenuated twice, the intensity of the reflectedambient light is reduced by approximately two thirds of that of thereceived ambient light. As an example, the green and blue portions ofthe incident ambient light 801 comprise approximately two thirds of theflux of the ambient light 801 entering a red subpixel. The green andblue portions of the incident ambient light 801 are blocked by thecontrast enhancement layer 810. Only the red portion of the ambientlight within the transmission band of the red filter material in thecontrast enhancement layer 810 transmits through the layer 810 and apart of the transmitted red ambient light is reflected back to theviewer. This part of the reflected ambient light is essentially the samecolor for the subpixel generated by the underlying color phosphor stripeand thus the color contrast is not adversely affected.

In FIG. 8, two adjacent filter stripes in the contrast enhancement layer810 can be separated by a stripe divider 830 made of either an opticalreflective and opaque material or an optical absorbent material.Reflective dividers 830, like other stripe dividers described in thisapplication, can be used to maximize the light output of the screen. Forexample, reflective white materials such as barium sulfate or TiO2pigments can be used to form the stripe dividers 830. Other lambertianwhite materials may also be used to form the stripe dividers 830. Theside walls of the stripe dividers may be a metallized reflective layer.One way to achieve a highly efficient reflective layer that is thin forthe stripe dividers 830 is to coat a sidewall with a metallizedunderlayer and to further place a white pigment filled layer over themetallized underlayer. Absorbing dividers 830 can be used to providecolor isolation and pixel separation but the screen output efficiencymay be less than that of the reflective dividers due to the loss oflight by absorption of the sidewalls. In some implementations, a stripedivider 830 can include both reflective and absorbent portions. Forexample, a stripe divider 830 can have white reflective and opaque sidewalls, a white reflective facet towards the excitation side of thescreen to provide optical reflection for the servo feedback, and ablackened absorbent facet towards the viewer side of the screen toreduce reflection towards the viewer and to improve the contrast.

The above use of a color-selective absorbent material in the contrastenhancement layer 810 for each subpixel to enhance the display contrastcan also be implemented by mixing such a material with thelight-emitting fluorescent material in each subpixel without a separatecontrast enhancement layer. In one implementation, each phosphor regionin the non-overlapping multi-layer design in FIG. 6 can be formed of amixture of a fluorescent material and a color-selective absorbentmaterial that transmits light emitted by the fluorescent material andabsorbs light of other colors. Hence, the contrast enhancing feature isbuilt into each subpixel to reduce the reflected ambient light to theviewer.

FIG. 9 shows another implementation that uses a phosphor layer 910 thatuses red, green and blue phosphor materials with built-incontrast-enhancing capability for emitting red, green and blue light,respectively, in a common fluorescent layer 910 of parallel fluorescentstripes. Consider three consecutive red, green and blue phosphor stripes911, 912 and 913. The material for the red phosphor stripe 911 is amixture of a red phosphor emitting red light and a red ink or pigmentwhich transmits the red light and absorbs other light including thegreen and blue light. Similarly, the material for the green phosphorstripe 912 is a mixture of a green phosphor emitting green light and agreen ink or pigment which transmits the green light and absorbs otherlight including the red and blue light; and the material for the bluephosphor stripe 913 is a mixture of a blue phosphor emitting blue lightand a blue ink or pigment which transmits the blue light and absorbsother light including the red and green light. This contrast-enhancingphosphor layer 910 can be combined with various screen designs andconfigurations described in this application.

In some implementations, the contrast enhancement layer 810 in FIG. 8can be replaced by a filter layer that blocks transmission of theexcitation light and uniformly attenuates visible light at the visiblecolors emitted by the fluorescent layer. Hence, to the excitation light,this filter layer is opaque and prevents any excitation light to appearon the viewer side of the screen; to the visible light, the filter layerbehaves like a neutral density (ND) filter to attenuate the visiblelight including the reflected ambient light. Because ambient light thatis reflected towards the viewer passes through this filter layer twice,the attenuation to the reflected ambient light is twice as much as thelight generated by the fluorescent layer. Therefore, the contrast of theimages displayed by emitted visible light in the fluorescent screen isenhanced in comparison with the same screen without the filter layer.Such an excitation light blocking ND filter layer can be less expensivethan the contrast enhancement layer 810 formed of color filters. Forexample, this excitation light blocking ND filter layer may be apolyester layer that blocks radiation from 400 nm to 415 nm with atransmission less than 0.01% for light below 410 nm and a transmissionof greater than 50% for light above 430 nm. The optical attenuation ofthe polyester layer can be approximately uniform for visible lightbetween 430 nm and 670 nm. The actual amount of the attenuation of thisfilter layer can be selected based on specific requirements for aparticular screen and may be above 50% in some designs and below 50% inother designs. The optical blocking function of this filter layer may beseparately implemented from the neutral density filtering function.Hence, two separated layers, one excitation light blocking layerdesigned to block the excitation light and another neutral densityfilter layer to uniformly attenuates the visible light, can beimplemented on the viewer side of the fluorescent layer in the screen.

The above described fluorescent screens use different phosphor materialsin different fluorescent stripes to produce different colors underexcitation of the excitation light. Alternatively, different fluorescentstripes can be formed by the same fluorescent material that emits whitelight and can further include color filters to produce desired differentcolors from the fluorescent light. The contrast enhancement layer 810 inFIG. 8 can be used to implement such color filters so that each colorfilter achieves both contrast enhancement and generation of a designatedsubpixel color.

FIG. 10 illustrates an example of a fluorescent screen design that has acontiguous and uniform layer 1000 of mixed phosphors. This mixedphosphor layer 1000 is designed and constructed to emit white lightunder optical excitation of excitation light. The mixed phosphors in themixed phosphor layer 1000 can be designed in various ways and a numberof compositions for the mixed phosphors that emit white light are knownand documented. Other non-phosphor fluorescent materials that emit whitelight can also e used for the layer 1000. As illustrated, a layer 810 ofcolor filters, such as stripes of red-transmitting, green-transmittingand blue-transmitting filters, is placed on the viewer side of the mixedphosphor layer 1000 to filter the white light and to produce coloredoutput towards the viewer. In this example, the layers 1000 and 810 aresandwiched between substrates 1001 and 1002. The color filters in thelayer 810 may be implemented in various configurations, including indesigns similar to the color filters used in color LCD panels. In eachcolor filter region e.g., a red-transmitting filter, the filtertransmits the red light and absorbs light of other colors includinggreen light and blue light. Two adjacent color filters may be separatedby a divider 830 such as a reflective or absorbent separator 404.

The screen structure in FIG. 10 is simpler than other screen designswith different fluorescent stripes because the mixed phosphor layer 1000in FIG. 10 is a contiguous layer without striped spatial structures.This construction avoids alignment issues associated with aligning thefilters in layer 810 with respective fluorescent stripes in the layer820 in FIG. 8. The substrate 1001 receives the excitation light and thuscan be made of a material transparent to the excitation light, e.g.,violet or UV light. The substrate 1002 faces the viewer and can be madeof a material transparent to the colored light filtered by the filtersin the layer 810. In fabrication, the layer 810 can be fabricated on thesubstrate 1002 and the layer 1000 can be fabricated on the substrate1001. The two substrates 1001 and 1002 can be engaged to each other toform the screen. At the output surface of the second substrate 1002, ananti-reflection coating (AR) may be formed to improve the lighttransmission to the viewer. In addition, a hard protection layer may beformed over the second substrate 102 to protect the screen surface.

The excitation beam 120 in the above described systems can enter thefluorescent layer of the screen at a varying angle during a scan. Thescanning causes the incident angle of the excitation beam 120 to thescreen to change during each horizontal scan across different positionson the screen. For some screen constructions, the efficiency of thescreens may be sensitive to the incident direction of the excitationbeam 120 and some screen designs prefer the direction of the excitationbeam 120 to be close to the normal direction to achieve a highefficiency of coupling the excitation light into the fluorescent layer.In one implementation for controlling the incident angle of theexcitation beam 120 to the fluorescent layer, an optical mechanism maybe implemented at the entry to the screen, e.g., the entrance layer 411in FIG. 4, to direct the incident excitation beam 120 to be normal orapproximately normal to the screen. One example of the entrance layer411 is a Fresnel lens layer.

FIG. 11 shows an example of a screen with a Fresnel lens layer 1110formed at the entry side of the screen to cover the entire area of thescreen that receives the excitation beam 120. The Fresnel lens layer1110 can be formed in a dielectric substrate that may be made of, e.g.,a glass or a plastic material. An acrylic plastic material, for example,may be used to form the Fresnel lens layer 1110. A dielectric layer 1112with a different index than the Fresnel lens layer 1110 can be formedbetween the Fresnel lens layer 1110 and the remaining portion of thescreen to create a difference in the refractive index from the Fresnellens layer 1110 to the next layer of the screen, e.g., the firstdichroic layer 412. The layer 1112 can be an air gap or a dielectricmaterial transparent to the excitation light. The remaining portion ofthe screen includes the fluorescent layer 400 and other layers of thescreen. A dichroic filter layer (D1) 412 on the excitation side of thefluorescent layer 400 can be implemented. In addition, an encapsulationlayer 1120, a screen gain layer 423, a contrast enhancement layer 422,and a second dichroic layer D2 421 (a UV blocker) may also be providedin the screen. An anti-reflection layer 640 can be formed on theentrance surface of the Fresnel lens layer 1110 for receiving theexcitation beam 120 with a minimized loss due to reflection.

In some implementations of the screen in FIG. 11, the first dichroiclayer 421 (D1) can be designed to transmit light from 405 nm to 410 nmwith a transmission of about 99.75% and to reflect visible light from440 nm to 410 nm with a reflectivity of about 95%; the anti-reflectionlayer 640 can be designed to transmit UV light at 405 nm with atransmission of about 99.75%. The screen gain layer 423 can be designedto optically enhance the brightness and enlarge the viewing angle of thescreen and may include a lenticular layer with lens elements, adiffractive optic layer of diffractive elements, a holographic layerwith holographic elements, or a combination of these and otherstructures. The contrast enhancing layer 422 can include acolor-selective absorbing pigment or dye supported in a base medium ormatrix in each subpixel to absorb ambient light and to transmit light inthe color of that subpixel. The spatial order of the encapsulation layer1120, the screen gain layer 423, the contrast enhancement layer 422 andthe UV-blocking dichroic layer 421 (D2) may vary with screen designs.

FIG. 12 illustrates the operation of the Fresnel lens layer 1110 in FIG.11. The Fresnel lens layer 1110 has Fresnel rings and can be configuredto redirect the incident scanning excitation beam 120 via opticaldiffraction, refraction or both as the incident excitation beam 1210that is approximately normal to the screen. The Fresnel lens layer 1110can be in a telecentric configuration for the incident scanningexcitation beam 120.

The above Fresnel lens layer 1110 controls the incident direction of theexcitation beam 120 into the remaining portion 1220 of the screen. Oncethe excitation beam 120 enters the screen, the excitation light shouldbe fully utilized to excite the fluorescent layer and to generatevisible light for displaying images to the viewer. Inside the screen, aportion of the excitation light can be redirected back towards theexcitation side of the screen due to scattering and reflection byvarious surfaces and other screen structures within the screen. Suchscattered and reflected excitation light should be recycled by directingit back to the fluorescent layer. In addition, a portion of the emittedvisible light from the fluorescent layer can also propagate towards theexcitation side of the screen and would cause loss of the imagebrightness if not being redirected to the viewer.

The entrance layer 411 in FIG. 4 can include a prismatic layer toreflect backward propagating excitation light and visible light, thatpropagates towards the entrance layer from the fluorescent layer, backto the fluorescent layer. Such a prismatic layer has parallel periodicprism stripes with apexes of a predetermined apex angle (e.g., 90degrees) to form angled facets to direct the received excitation beam120 into the screen by refraction. Each apex has two opposing angledfacets that refract and reflect light and hence parallel rays in acommon incident direction are refracted or reflected into two groups ofparallel rays into two directions away from each other. The prismaticlayer reflects light in various directions propagating from thefluorescent layer of the screen towards the prismatic layer back to thefluorescent layer by reflection at the angled facets including the totalinternal reflection for rays at incident angles into the angled facetsgreater than the critical angle for the total internal reflection angle.The reflected excitation light is recycled back to the fluorescent layerto further excite the fluorescent layer and thus the utilization of theexcitation light for generating the visible fluorescent light isenhanced. In addition, the fluorescent light propagating towards theprismatic layer is also reflected towards the fluorescent layer and theviewer to enhance the brightness of the screen perceived by the viewer.

FIG. 13 shows one implementation of a fluorescent screen having aprismatic layer 1310 and an adjacent screen layer 1320 within thescreen. The screen layer 1320 can be a fluorescent layer as shown andcan be another layer on the excitation side of the fluorescent layer.The prismatic layer 1310 includes an array of prism elements 1311, e.g.,an array of prism stripes having angled facets 1312 with an apex angleat 90 degrees. The angled facets 1312 are used to receive the excitationlight 120. The width of each prism stripe can be greater than thewavelength of the excitation light and can be less than the width ofeach fluorescent stripe, i.e., the width of one subpixel of the screen.A cross sectional view is shown in FIG. 13 where the parallel prismstripes are perpendicular to the cross section.

The prismatic layer 1310 can be aligned to place the prism stripesparallel to the fluorescent stripes in the fluorescent layer 1320 in aparallel configuration or perpendicular to the fluorescent stripes in across configuration. In each prism stripe, the two angled facets 1312,which intersect with each other at the prism apex 1313, refract orreflect light parallel rays into two groups of parallel rays into twodifferent directions in a plane perpendicular to the prism stripes. Inthe cross configuration, the two split beams that are split from theexcitation beam 120 are directed to two locations within the samefluorescent stripe and hence does not cause spatial spreading of theexcitation light along a direction perpendicular to the fluorescentstripes. As a result, the cross configuration can be used to preventlight of the excitation beam 120 from entering two adjacent fluorescentstripes at the same time. Recall that the excitation beam 120 is turnedon to illuminate one fluorescent stripe to address one subpixel at atime. When a portion of an optical pulse in the excitation beam 120intended to address one fluorescent stripe is split by the prism stripeand is directed to an adjacent fluorescent stripe, a cross talk betweentwo adjacent subpixel occurs and can lead to degradation in color purityand image resolution. This can occur when the prismatic layer 1310 is inthe parallel configuration where the splitting of the excitation beam120 by each prism stripe is along the direction perpendicular to thefluorescent stripes. In the parallel configuration, the visiblefluorescent light generated in one fluorescent stripe that propagatestowards the prismatic layer 1310 can also have a higher probability ofbeing reflected by the angled prim facets into an adjacent fluorescentstripe.

FIG. 13A shows operation of a prism stripe 1311 of the prismatic layer1310 in coupling the excitation beam 120 into the screen. The two angledfacets 1312 are separated identified as facets 1312A and 1312B whichinterest at the apex 1313. In the xyz coordinate shown, the prism stripeis placed to be parallel to the y direction. The excitation beam 120,shown in a normal incidence to the prismatic layer 1310, is split by thefacets 1312A and 1312B as two beams 120A and 120B, respectively. The twobeams in the two different directions arrive the fluorescent layer 400at two different locations x1 and x2 along the x direction. This featureof the prism stripe creates double imaging. Hence, in the crossconfiguration where the prism stripes are along the y direction and thefluorescent stripes in the fluorescent layer 400 are in the x direction,the locations x1 and x2 are two different locations along thelongitudinal direction of the fluorescent stripe and thus are the samefluorescent stripe. In the parallel configuration where the prismstripes and the fluorescent stripes are parallel and are all along the ydirection, the two locations x1 and x2 are separated from each otheralong the direction perpendicular to the longitudinal direction of afluorescent stripe and thus can fall in two adjacent fluorescentstripes. The amount of the separation between the two beams 120A and120B at the fluorescent layer 400 depends on the thickness of theprismatic layer 1310 and the distance between the fluorescent layer 200and the prismatic layer 1310. Both alignment configurations for theprismatic layer 1310 can be used and the cross configuration may bepreferred in some screen designs. In either configuration, the thicknessof the prismatic layer can be minimized to minimize the effect of thedouble imaging of the prism stripe on the fluorescent layer.

The prismatic layer 1310 can be formed in a dielectric layer that istransparent to the excitation light 120 and has a refractive index n2greater than the refractive index n1 of the transparent material abovethe angled facets 1312. The material above the angled facets 1312 can beair or a low-index transparent material. The material for the prismaticlayer 1310 is selected to have a large refractive index n2 so that asmall critical angle θ_(cr)=arcsin(n₁/n₂) for the total internalreflection (TIR) is achieved at the angled facets 1312. The angledfacets 1312 is used to receive the excitation light 120.

Depending on the screen designs, the screen layer next to the prismaticlayer 1310 can be selected from various layers, e.g., an air gap, a lowindex layer with a lower refractive index than that of the prismaticlayer, or a high index layer with a higher refractive index than that ofthe prismatic layer. In the specific example illustrated in FIG. 13,behind the prismatic layer 1310 is a layer 1320 that has a refractiveindex n3 that is approximately equal to the refractive index of theprismatic layer 1310. The index matching condition reduces undesiredoptical reflection at the interface between the prismatic layer 1310 andthe layer 1320 and thus reduces the optical loss of the excitation light120. The layer 1320 can be a dielectric layer that is transparent toexcitation light 120 and is located between the prismatic layer 1310 andthe fluorescent layer of the screen. The layer 1320 can also be thefluorescent layer which is formed by a layer of a binder material inwhich the fluorescent particles are embedded.

In operation, the scanning excitation light 120 is refracted by theangled facets when entering the prismatic layer 1310 and the refractedexcitation light enters the screen to excite the fluorescent layer whichgenerates visible fluorescent light to display images. A portion of theexcitation light that is not absorbed and a portion of the fluorescentlight can propagate towards the prismatic layer 1310. Although suchlight in all angles is reflected by the angled facets, a portion of suchlight can be totally reflected back into the screen at the angled facetsby the total internal reflection (TIR) for rays with incident anglesgreater than the TIR critical angle. The reflected excitation light isthus recycled by interacting with the phosphor layer again and causingthe phosphor to radiate the fluorescent light. The reflected fluorescentlight is scattered by the phosphor, a portion of which exits from theviewing side. Thus, the prismatic layer 1310 improves utilization of theexcitation light and enhances the brightness on the viewing side of thephosphor screen.

Notably, the prism apex angle and the index of the prismatic layer 1310can be selected so that backward propagating light rays at or near thenormal incidence to the screen have incident angles at each angled facet1312 that are at or greater than the TIR critical angle for that angledfacet 1312. Light ray 1341 as shown is one example of such a ray and istotally reflected at a respect angled facet 1312. The normal directionfor each angled facet 1312 is different from the normal direction of thescreen and forms an angle with the normal direction of the screen by onehalf of the prism apex angle. Light ray 1342 as shown is incident to anangled facet 1312 at an angle around one half of the prism apex anglewith respect to the normal direction of the screen plane and thus isnear the normal incidence for that angled facet 1312. This light ray1342 thus is partially reflected and the rest of the light transmitsthrough the prismatic layer. The transmitted portion of the light ray1342 is lost and represents the loss for the screen. As a result, theprismatic layer 1310 can totally reflect backward propagating light raysincident at a wide range of angles, including light rays at the normalincidence to the screen and large angles. Light rays incident to theprismatic layer 1310 around the one half of the prism apex angle,however, are not totally reflected and are only partially reflected.

The entrance layer 411 can be implemented by using a flat layer formedof a high-index material n2 that is transparent to the excitation light120 in lieu of the prismatic layer 1310. FIG. 14 shows an examplehigh-index layer 1410. The substrate or rigid layer 630 in FIG. 6 isalso an example of such an entrance layer. The entrance surface of thelayer 1410 is flat and the reflection at the entrance surface 1412including the TIR can direct both backward propagating excitation lightand the fluorescent light back into the screen to recycle the excitationlight and to “push” more fluorescent light to the viewer side of thescreen. This function of the flat high-index layer 1410 is similar tothe prismatic layer 1310. The index n2 of the flat layer 1410 should beas high as possible to make the TIR critical angle at the entrancesurface 1412 as small as possible to increase the total reflection.Different from the prismatic layer 1310, the normal direction of theentrance surface 1412 is the normal direction of the screen and thuslight rays incident at or near the normal incidence to the screen withincident angles less than the TIR critical angle at the surface 1412 arepartially reflected and partially transmitted. Light rays with incidentangles with respect to the normal incidence of the screen greater thanthe TIR critical angle are totally reflected. In certain implementationsof the prismatic layer 1310 in FIG. 13 or the high-index layer 1410 inFIG. 14 as an entrance layer to the screen, the index-matched layer 1320next to the layer 1310 or 1410 may be replaced by a low index layer withan index less than the player 1310 or 1410, such as an air gap or alow-index dielectric layer.

The above prismatic layer 1310 and the high-index layer 1410 havedifferent TIR properties, including different angular responses inreflecting light incident at different angles. Hence, the prismaticlayer 1310 in FIG. 13 and the high-index layer 1410 in FIG. 14 may becombined together on the excitation side of the fluorescent layer toincrease the optical throughput of the screen. In one implementation,the prismatic layer 1310 in FIG. 13 and the high-index layer 1410 inFIG. 14 may be spaced from each other by an air gap or a low-index layeras the entrance layer for the screen. The prismatic layer 1310 reflectslight at small incident angles via the total internal reflection whilethe high-index layer 14109 reflects light at large incident angles viathe internal total reflection. For example, the layers 1310 and 1410 canbe used as part of the entrance layer and are spaced from each other bya low index layer or an air gap. The prismatic layer 1310 can be thefirst layer to receive the excitation beam 120 which transmits throughthe air gap or low-index layer into the layer 1410 or the layer 1410 canbe the first layer to receive the excitation beam 120 which transmitsthrough the air gap or low-index layer into the prismatic layer 1310.The surface 1412 of the layer 1410 is designed to have an TIR criticalangle that is less than the TIR critical angle for each angled facet1312 of the prismatic layer 1310 so that light rays that are partiallyreflected by the prismatic layer 1310 are totally reflected by the layer1410. Under this configuration, the light rays at or near the formaldirection of the screen that are not totally reflected by the layer 1410are totally reflected by the prismatic layer 1310. Therefore, thiscombination of the layers 1310 and 1410 effectuates the function of thedichroic layer (D1) 412. The dichroic layer (D1) 412, when implementedby a multilayer structure as an interference filter, may be sensitive toincident angles where the dichroic function can be performed to lightrays at or near the normal incidence or within a limited angular rangefor the incidence angles. The above combination of layers 1310 and 1410is not sensitive to the incident angles and reflect backward propagatinglight at all angles. In addition, the spectral properties of amultilayer interference dichroic filter can be limited and can vary withthe incident angles of the beams. The above combination of layers 1310and 1410 is essentially free of such performance limitations of the amultilayer interference dichroic filter.

Fluorescent screens can be designed to combine the second dichroic layer421 (D2) on the other side of the fluorescent layer, the prismatic layer1310 or the high-index layer 1410 and the second dichroic layer 421 (D2)to confine a significant amount of the excitation light to bounce backand forth through the fluorescent layer between the prismatic layer 1310(or the high-index layer 1410) and the second dichroic layer 421 (D2) toimprove the utilization of the excitation light and the amount ofgenerated fluorescent light.

The following sections now describe some specific fluorescent screendesigns that implement selected screen elements described above.

FIG. 15 shows a multilayered fluorescent screen that implements aprismatic layer 1310 to couple excitation light into a fluorescent layer1570. The screen includes a transparent substrate 1510 that faces theviewer side and transmits the colored light carrying images to theviewer. An array of opaque subpixel stripe dividers 1520 are formed onone surface of the transparent substrate 1510 to define the fluorescentstripes and optically separate adjacent or neighboring fluorescentstripes (i.e., adjacent subpixels). The stripe dividers 1520 may be madeof a solid opaque film resist, an ink material printed on the substrate1510, or an optical reflective or absorbent material. Between the stripedividers 1520 are contrast enhancement color filters 1530 shaped asparallel stripes where three adjacent filers transmit three differentdesignated colors, respectively, and absorb light of other colorsdifferent from their designated colors. Three adjacent filters 1531,1532 and 1533 are examples for the filters 1530, where the filter 1531is a red-transmitting filter that absorbs light of green and blue, thefilter 1532 is a green-transmitting filter that absorbs light of red andblue, and the filter 1533 is a blue-transmitting filter that absorbslight of green and red. The operation and effect of the filters 1530 incombination with the fluorescent layer 1570 having fluorescent stripesemitting different fluorescent colors are described with reference toFIG. 8.

The screen in FIG. 15 includes a dielectric layer 1540 formed above andare supported by stripe dividers 1520 and below the fluorescent layer1570. The dielectric layer 1540 and the filters 1530 are spaced apart bya low-index layer or an air gap 1550 which has an index less than thatof the dielectric layer 1540. The height of the stripe dividers 1520 canbe used to control the thickness of the low-index layer or the air gap1550 which may be 10 to 50 microns. In some implementations, thedielectric layer 1540 can be a transparent material with a refractiveindex less than that of the fluorescent layer 1570 such as a clear PETplastic layer of about 50 microns. In other implementations, thedielectric layer 1540 can be a dichroic layer (D2) that transmitsvisible light and reflects the excitation light at a UV or violetwavelength. may be formed on top of the array of the stripe dividers andbelow the fluorescent layer.

The fluorescent layer 1570 in FIG. 15 can be repetitive differentparallel fluorescent stripes for emitting different fluorescent colors(e.g., red, green and blue) and is formed over the layer 1540. Spatiallycorresponding to the opaque subpixel stripe dividers 1520, a secondarray of stripe dividers 1560 are formed on the layer 1540 to physicallyseparate different fluorescent stripes 1570 so that each of thefluorescent stripe 1570 is aligned with a respective filter 1530.

The stripe dividers 1560 can be made from an optical reflective ordiffusive material to direct at least part of the incident excitationlight 120 back to the excitation side of the screen to be received byone or more servo photodetectors for a servo control of the displaysystem. The power of the reflected excitation light produced by thestripe dividers 1560 varies with the position of the beam on afluorescent stripe and thus can be used to determine a relative positionof the excitation beam 120 on the fluorescent stripe and can be used tocontrol the optical alignment between the excitation beam 120 andrespective fluorescent stripes during a horizontal scan. In thiscontext, the stripe dividers 1560 function as servo marks and arereflective at least at their facets facing the excitation side of thescreen. The stripe dividers 1560 can also be made to include anIR-emitting fluorescent material or other fluorescent material emittinglight at a wavelength different from the excitation light 120 and thevisible light emitted by the fluorescent layer 1570 that is excited bythe same excitation laser light 120 for the fluorescent layer 1570. Suchfluorescent stripe dividers 1560 can be used to improve the detectionsignal to noise ratio at the one or more servo photodetectors becausescattered excitation light and the visible fluorescent light generatedby the fluorescent layer 1570 can be filtered out to allow only the IRlight to be detected by the one or more servo photodetectors for theservo control operation. Details of the stripe dividers 1560 as servostripe marks and the servo control are described in a separate patentapplication.

On top of the fluorescent layer 1570 in FIG. 56, the prismatic layer1310 is formed to transmit the excitation laser light in the UV orviolet range and to reflect light, both the excitation light and thefluorescent light, from the fluorescent layer 1570. Hence, the prismaticlayer 1310 effectuates the function of the dichroic layer 412 (D1)described above for reducing loss of the fluorescent light to theexcitation side of the screen. In addition, the prismatic layer 1310also recycles the unabsorbed excitation light back to the fluorescentlayer 1570.

Notably, between the prismatic layer 1310 and the fluorescent layer1570, a low index transparent layer 1580 with an index less than that ofthe fluorescent layer 1570 is formed to increase the optical throughputof the screen. A polymer material or an air gap can be used as thesecond low index transparent layer 1580. Referring to precedingdescription for the prismatic layer 1310 in FIG. 13 and the flathigh-index layer 1410 in FIG. 14, the layers 1310 and 1410 can becombined to effectuate total internal reflection to backward propagatingrays at all angles. In FIG. 15, the fluorescent layer 1570 effectivelyprovide the function of the high-index layer 1410 in FIG. 14. Backwardpropagating light rays at incident angles to the interface between thelayers 1570 and 1580 greater than the TIR critical angle at thisinterface are totally reflected, including both the excitation light andthe fluorescent light generated in the layer 1570. Backward propagatinglight rays with incident angles less than the TIR critical angle at thisinterface are partially reflected by the interface and partiallytransmit through the layer 1580 to enter the prismatic layer 1310. Thisportion of the backward propagating light is then totally reflected bythe angles facets 1312 of the prismatic layer 1310.

FIG. 16 illustrates another screen based on the design in FIG. 15 wherea fluorescent layer 1610 of identical parallel stripes made of a singlemixture of different phosphors that emits white light is used to replacethe fluorescent layer 1570 with fluorescent stripes made of differentfluorescent materials. The color generation is achieved by using thecolor filters 1530 based on the design in FIG. 10.

FIG. 17 shows another example of a screen design with the prismaticlayer 1310 where a single array of stripe dividers 1710 are used toseparate both the parallel stripe color filters 1530 and parallelfluorescent stripes 1720 made of a single white-light-emittingfluorescent material or different fluorescent materials emittingdifferent colors. The separate array of stripe dividers 1560 as servomarks in the designs in FIGS. 15 and 16 is eliminated to simply thescreen structure. The single array of stripe dividers 1710 is used asboth stripe dividers and the servo marks and can be made of a materialfor the stripe dividers 1560. Different from the designs in FIGS. 15 and16, this example uses a low index transparent layer 1730 formed betweenand in direct contact with each color filter 1530 and the fluorescentlayer 1720. The low index transparent layer 1730 has a refractive indexless than that of the fluorescent material to increase the opticalthroughput into each color filter 1530 of the screen with reducedoptical loss caused by the total internal reflection at their interface.The layer 1730 may a gel layer that is sealed between the layers 1720and 1730. A second low index transparent layer 1580 with an index lessthan that of the prismatic layer 1310 and the fluorescent material isformed between the prismatic layer 1310 and the fluorescent layer 1720to increase the optical throughput of the screen. A polymer material oran air gap can be used as the second low index transparent layer 1580.

FIGS. 18 and 19 show two exemplary screens that use the high-index flatlayer 1410 in FIG. 14 as the entrance layer for the screen. In FIG. 18,the screen is based on the screen structures in FIGS. 15 and 16 and usesthe high index layer 1410 to replace the prismatic layer 1310 and thelow index layer 1580. In FIG. 19, the screen is based on the screenstructure in FIG. 17 and uses the high index layer 1410 to replace theprismatic layer 1310 and the low index layer 1580. layer.

FIG. 20 shows a fluorescent screen design where the dichroic layers 412(D1) and 421 (D2) are formed on two sides of the fluorescent layer 1720based on the design in FIG. 4. A low index transparent layer 2010 isformed between the dichroic layer 421 and the substrate 1510 to improvethe optical throughput to the viewer. An array of stripe dividers 1560are formed to separate adjacent fluorescent stripes and to also operateas the servo marks for the above servo feedback control as described inFIG. 15.

FIG. 21 shows a screen design based on the design in FIG. 17. A dichroiclayers 412 (D1) that transmits the excitation light 120 and reflectsfluorescent light emitted by the fluorescent layer 1720 is used toreplace the prismatic layer 1310. Parallel fluorescent stripes 1720 canbe made of a single white-light-emitting fluorescent material ordifferent fluorescent materials emitting different colors. The stripedividers 1710 are used to both physically separate adjacent fluorescentstripes and operate as servo marks for the above servo feedback controlas described with reference to FIG. 15.

FIG. 22 shows another screen design based on the design in FIG. 14. Arigid support substrate 2230, such as a transparent plastic or glassmaterial, is used as a base to support various screen layers with aplanar screen stack 2210. An optical grad acrylic substrate, forexample, can be used to form the substrate 2230. The planar screen stack2210 includes a film base layer 2202 which operates as the high-indexlayer 1410 shown in FIG. 14 to couple light into the screen and toreflect light back into the screen based on total internal reflection. Apolyester film, such as the commercially available DuPont Teijin filmand Mylar DL film, can be used as the layer 2202. A filter support layer2201, such as a protective liner, may be attached to the polyester film2202. This support layer 2201 may be used to protect film base layer2202 during the fabrication and can be removed after the screen is fullyassembled. The support layer 2201 may also be retained after thefabrication as a protection layer. A layer 1570 of fluorescent stripesis formed in contact with the film base layer 2202 and are divided bystripe dividers 2203. The dividers 2203 are optically reflective at itsfacets or sidewalls in contact with the film base layer 2202 and thefluorescent stripes in the fluorescent layer 1570. A dielectric layer1540 is formed above the stripe dividers 2203 and to form a spacebetween the layer 1540 and the fluorescent layer 1570. This space can bean air gap or be filled with a low index layer 1730 with a refractiveindex less than that of the fluorescent regions in the fluorescent layer1570. A contrast enhancement layer 1530 with different color filters isformed on the layer 1540. An adhesive layer 2220, e.g., an opticallyclear laminating adhesive, is used to adhere the planar screen stack2210 to the substrate 2230. At the exit surface of the substrate 2230that faces the viewer, an anti-reflection layer 2240 can be formed toreduce the glare of the screen due to reflection of ambient light.

FIG. 23 shows details of the stripe dividers 2203 according to oneimplementation. All dimensions are in microns and are exemplary. Thebody of each divider 2202 is optically reflective and can be made of anoptical reflective material. As an option, the divider facet that facesthe viewer side of the screen can be coated with a blackened absorptivelayer 2310 to reduce any reflection towards the viewer side, e.g., lessthan 10% in reflection and greater than 80% in absorption from 400 nm to650 nm. This feature can enhance the resolution and contrast of thescreen. Various optically reflective materials can be used to form thedividers 2203. Metal materials such as aluminum can be used to constructthe dividers 2203 or as coating materials to form a coating on a surfaceor facet of each divider that needs to be reflective. In addition, awhite paint material can also be used to form the dividers 2203 toachieve a high reflectivity. For example, a white paint made of aTiO2-filled resin or a barium sulfate-filled resin can be formulated toachieve superior reflective properties to metal coatings, especiallywhen reflecting back into a clear polymer. The reflectivity of the whitepaint material can be grater than 90% from 400 nm to 650 nm.

Furthermore, the stripe dividers 2203 can also be made to include anIR-emitting fluorescent material or a fluorescent material emittinglight at a wavelength different from the excitation light 120 and thevisible light emitted by the fluorescent layer 1570 that is excited bythe same excitation laser light 120 for the fluorescent layer 1570. Suchfluorescent stripe dividers 2203 can be used to improve the detectionsignal to noise ratio at the one or more servo photodetectors becausescattered excitation light and the visible fluorescent light generatedby the fluorescent layer 1570 can be filtered out to allow only the IRlight to be detected by the one or more servo photodetectors for theservo control operation. The facet on each divider 2203 facing theviewer side can be coated with the absorptive layer 2310.

FIGS. 24 and 25 show two example screen designs that replace a colorfilter based contract enhancement layer with a filter layer that blocksthe excitation light and uniformly attenuates visible light to enhancethe display contrast. In FIG. 24, a planar screen stack 2410 replacesthe stack 2210 in FIG. 22. The stack 2410 includes a filter layer 2413which blocks excitation light (e.g., light between 400 nm and 415 nm)from transmitting to the viewer side and uniformly attenuates thevisible light, e.g., from 430 nm to 670 nm, as an ND filter. A polyesterfilm can be used as the filter layer 2413. Two optically clearlaminating adhesive layers 2411 and 2412 are used to engage the filterlayer 2412 to the stripe dividers 2203 on one side and to the substrate2230 on the other side.

In FIG. 25, a rigid support substrate 2520 is used to provide theexcitation blocking function and the ND filtering function of the filterlayer 2413 in FIG. 24, thus eliminating the filter layer 2413. Thissimplifies the screen construction. The planar screen stack 2510 in thisexample includes a laminating adhesive layer 2511, the stripe dividers2203, the fluorescent layer with fluorescent stripes 1570, the low indexlayer 1730 between the fluorescent layer and the laminating adhesivelayer 2511 and the high-index film base layer 2202.

In some of the screen designs, one or more layers may be a contiguouslayer across the fluorescent stripes without being divided into stripesby the stripe dividers. For example, the film base layer 2202 in FIGS.22, 24 and 25, and the dielectric layer 1540 in FIGS. 15, 16, 18 and 22,the capsulation layer 1120, the gain layer 423 in FIGS. 4 and 11 and thehigh-index layer 1401 in FIGS. 14, 18, 22, 23, 24 and 25 are such acontiguous layer. In such a contiguous layer, emitted visible light fromthe fluorescent light can be reflected back and forth at the twosurfaces of the contiguous layer and thus may be reflected into anadjacent subpixel to cause smear of images. In addition, excitationlight targeted at one subpixel may also be reflected into an adjacentsubpixel to excite a wrong color at the adjacent subpixel to cause aundesired halo effect. One way to reduce these adverse effects is tolimit the thickness of such a contiguous layer to a value less than awidth of a subpixel, e.g., 10 times less than the width of a subpixelalong the horizontal direction that is perpendicular to the fluorescentstripes.

In the above screen designs, the colored fluorescent light emitted fromthe phosphor layer passes through various interfaces between twodifferent layers or materials in the path towards the viewer. At each ofsuch interfaces, a difference in the refractive indices at the two sidesof the interface causes undesired reflection. In particular, the totalinternal reflection can occur at an interface when the emitted coloredlight propagates from a layer with an index higher than the next layerwhen the incident angle is greater than the critical angle of thatinterface. Therefore, in some implementations, the optical materials maybe selected to have refractive indices as close as possible to minimizethe reflection. In other implementations, a difference in refractiveindices at an interface is intentionally created to achieve certaineffects.

For example, the fluorescent layer in some of the fluorescent designscan have an adjacent low-index dielectric layer with a low refractiveindex on the viewer side of the fluorescent layer. The refractive indexof the low-index dielectric layer is less than the index of thefluorescent layer and the index of another screen layer that is incontact with the low-index dielectric layer. FIG. 26 illustrates anexample of this structure as part of a fluorescent screen. This exampleshows only a part of the screen to illustrate three consecutive screenlayers of this structure: a fluorescent layer 2600, a low-indexdielectric layer 2610 and a screen layer 2620 as the viewer-side outerlayer of the screen. Fluorescent light emitted in the fluorescent layer2600 can transmit through the low-index dielectric layer 2610 and thescreen layer 2610 to exit the screen and to reach the viewer. Thestructure in FIG. 26 can use the low-index dielectric layer 2610 toincrease the throughput of the fluorescent light from the fluorescentlayer 2600 to the viewer side of the screen and to reduce cross talkbetween two adjacent fluorescent stripes in the fluorescent layer 2600caused by reflection of the fluorescent light on the viewer side of thefluorescent layer 2600.

In this design, most of the fluorescent light propagating inside thefluorescent layer 2600 towards the layer 2610 partially transmits and ispartially reflected at the interface 2601 between the layers 2600 and2610. Because the index of the low-index dielectric layer 2610 is lessthan the fluorescent layer 2600, a portion of the fluorescent light thatarrives at the interface an angle greater than the critical angle forthe total internal reflection (TIR) is completely reflected back to thefluorescent layer 2600. Hence, the TIR condition creates an angularfiltering function at the interface 2601 to allow transmission offluorescent light with small incident angles less than that of the TIRcritical angle and to block transmission of fluorescent light withlarger incident angles. At the interface 2611 between the layers 2610and 2620, there is no total internal reflection towards the layer 2610because the index of the layer 2610 is less than that of the layer 2620.The fluorescent light at all angles partially transmits through theinterface 2611 to enter the layer 2620 and is partially reflected backto the layer 2610. Because the TIR condition at the interface 2601limits the angles of the fluorescent light entering the layer 2610 to beless than the TIR critical angle at the interface 2601, a fluorescentlight ray 2632 in the layer 2620 that is the transmission of the lightray 2631 in the layer 2631 also has a maximum angle determined by theindices of the layers 2600, 2610 and 2620. The layer 2620 has an exitsurface 2621 that is also the screen surface to interface the air.Accordingly, a total internal reflection can occur to light in the layer2620 with an incident angle greater than the TIR critical angle at theinterface 2621.

The TIR at the interface 2621, however, reduces the amount offluorescent light that exits the screen towards the viewer. This reducesthe screen brightness. In addition, the reflected light by the TIR atthe interface 2621 may cause fluorescent light in one color generated byone fluorescent stripe to enter an adjacent fluorescent stripe of adifferent color and thus lead to cross talk between two adjacentfluorescent stripes. For example, the blue light from a blue fluorescentstripe can excite the red and green fluorescent stripes to emit light.When this cross talk occurs, a blue spot on the screen can cause glowingin adjacent red and green pixels, often known as an image halo. As aresult, this TIR at the interface 2621 can cause degradation in colorpurity and the image resolution.

In recognition of at least the above, the indices of the layers 2600,2610 and 2620 can be selected so that a fluorescent light ray 2630 inthe fluorescent layer 2600 that originates the light ray 2631 in thelayer 2610 and the light ray 2632 in the layer 2620, when at an incidentangle equal to the TIR critical angle at the interface 2601, leads tothe incident angle of the light ray 2632 at the exit surface 2621 of thelayer 2620 to be no greater than the TIR critical angle at the interface2621. Under this condition, the fluorescent light that transmits throughthe interface 2601 from the fluorescent layer 2600 into the low-indexlayer 2610 will not be totally reflected at the interface 2621. Notably,the low-index layer 2610 can be an air gap which has the lowest index ora dielectric material with a desired low index. This feature has beenshown in some of the examples described above, including screens inFIGS. 15, 16, 18, 22, 24 and 25.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of an invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or a variation of a subcombination.

Only a few implementations are disclosed. However, it is understood thatvariations and enhancements may be made.

1. A display screen, comprising: a plurality of parallel screen layerswhich are engaged to form a planar stack and comprise: a fluorescentlayer absorbing excitation light at an excitation wavelength to emitvisible light at a different visible wavelength; and a prismatic layercomprising a plurality of prism elements which receive and couple theexcitation light to the fluorescent layer.
 2. The display screen as inclaim 1, further comprising: a low-index layer formed on a side of andin contact with the fluorescent screen that is opposite to the prismaticlayer and having a refractive index less than a refractive index of thefluorescent layer; and a screen layer in contact with the low-indexlayer and having a refractive index higher than the refractive index ofthe low-index layer.
 3. The display screen as in claim 2, wherein: thelow-index layer is an air gap.
 4. The display screen as in claim 1,wherein: the fluorescent layer comprises a plurality of parallelfluorescent stripes; and wherein the display screen further comprises aplurality of parallel stripe dividers each located between two adjacentfluorescent stripes.
 5. The display screen as in claim 4, wherein: thestripe dividers comprise a white paint that is optically reflective andopaque.
 6. The display screen as in claim 5, wherein: the white paintcomprises a mixture of a resin with either TiO₂ or Barium Sulfate. 7.The display screen as in claim 4, wherein: each stripe divider comprisesa fluorescent material that emits fluorescent light at a wavelengthdifferent from the excitation light and the visible light.
 8. Thedisplay screen as in claim 4, wherein: each stripe divider comprises areflective metal coating.
 9. The display screen as in claim 4, wherein:at least three adjacent fluorescent stripes of the plurality of thefluorescent stripes are made of, respectively, a first fluorescentmaterial to absorb the excitation light to emit first visible light of afirst color, a second fluorescent material to absorb the excitationlight to emit second visible light of a second color, and a thirdfluorescent material to absorb the excitation light to emit thirdvisible light of a third color.
 10. The display screen as in claim 4,wherein: each fluorescent stripe comprises a fluorescent material thatabsorbs the excitation light and emits white light; and wherein thescreen layers further comprise a filter layer comprising a plurality ofparallel filter stripes each aligned to a corresponding fluorescentstripe along a direction perpendicular to the to the screen layers, andwherein the fluorescent layer is located between the prismatic layer andthe filter layer, and wherein at least three adjacent filter stripes arerespectively made of a first filter material to transmit first visiblelight of a first color while absorbing light of other colors including asecond color and a third color, a second filter material to transmitsecond visible light of the second color while absorbing light of othercolors including the first and the third colors, and a third filtermaterial to transmit third visible light of the third color whileabsorbing light of the other colors including the first and the secondcolors.
 11. The display screen as in claim 4, wherein: the screen layersfurther comprise a filter layer comprising a plurality of parallelfilter stripes each aligned to a corresponding fluorescent stripe alonga direction perpendicular to the screen substrate, the fluorescent layerlocated between the prismatic layer and the filter layer, and at leastthree adjacent filter stripes are respectively made of a first filtermaterial to transmit first visible light of a first color whileabsorbing light of other colors including a second color and a thirdcolor, a second filter material to transmit second visible light of thesecond color while absorbing light of other colors including the firstand the third colors, and a third filter material to transmit thirdvisible light of the third color while absorbing light of the othercolors including the first and the second colors.
 12. The display screenas in claim 11, wherein: the screen layers further comprise a pluralityof second parallel stripe dividers each located between two adjacentfilter stripes.
 13. The display screen as in claim 12, wherein: thescreen layers further comprise a dielectric layer between thefluorescent layer and the filter layer, and the stripe dividers are incontact with the dielectric layer to separate the dielectric layer andthe filter layer from each other by a gap.
 14. The display screen as inclaim 13, wherein: the gap between the filter layer and the dielectriclayer is filled with a low-index dielectric material having a refractiveindex less than a refractive index of the dielectric layer.
 15. Thedisplay screen as in claim 13, wherein: the gap between the filter layerand the dielectric layer is filled with air.
 16. The display screen asin claim 4, wherein: the screen layers further comprise a filter layercomprising a plurality of parallel filter stripes each formed betweentwo adjacent stripe dividers to align with a corresponding fluorescentstripe between the two adjacent stripe dividers, the fluorescent layerlocated between the prismatic layer and the filter layer, at least threeadjacent filter stripes are respectively made of a first filter materialto transmit first visible light of a first color while absorbing lightof other colors including a second color and a third color, a secondfilter material to transmit second visible light of the second colorwhile absorbing light of other colors including the first and the thirdcolors, and a third filter material to transmit third visible light ofthe third color while absorbing light of the other colors including thefirst and the second colors.
 17. The display screen as in claim 16,wherein: the screen layers further comprise a dielectric layer betweenthe prismatic layer and each fluorescent stripe and the dielectric layerhas a refractive index less than a refractive index of the fluorescentstripe.
 18. The display screen as in claim 16, wherein: the screenlayers further comprise a dielectric layer between each filter stripeand a corresponding fluorescent stripe.
 19. The display screen as inclaim 1, wherein: the fluorescent layer comprises a uniform layer of afluorescent material that absorbs the excitation light and emits whitelight; the screen layers further comprise a filter layer comprising aplurality of parallel filter stripes, the fluorescent layer beinglocated between the prismatic layer and the filter layer; and at leastthree adjacent filter stripes are respectively made of a first filtermaterial to transmit first visible light of a first color whileabsorbing light of other colors including a second color and a thirdcolor, a second filter material to transmit second visible light of thesecond color while absorbing light of other colors including the firstand the third colors, and a third filter material to transmit thirdvisible light of the third color while absorbing light of the othercolors including the first and the second colors.
 20. The display screenas in claim 1, wherein: the screen layers further comprise a filterlayer formed on one side of the fluorescent layer that is opposite to aside where the prismatic layer is located, the filter layer blockstransmission of the excitation light and transmits the visible lightwith an attenuation that is uniform over a spectral range of the visiblelight.
 21. The display screen as in claim 1, wherein: the screen layersfurther comprise: a selective blocking layer that transmits the visiblelight and blocks the excitation light, and a neutral density filterlayer that attenuates the visible light with an attenuation uniform overa spectral range of the visible light; and the selective blocking layerand the neutral density filter layer are located at a side of thefluorescent layer that is opposite to the side where the prismatic layeris located.
 22. The display screen as in claim 1, wherein: the prismaticlayer is a first layer that receives the excitation light and is spacedfrom an adjacent screen layer by an air gap.
 23. The display screen asin claim 1, wherein: the prismatic layer comprises a plurality ofparallel prismatic stripes, and the fluorescent layer comprises aplurality of parallel fluorescent stripes that are perpendicular toparallel prismatic stripes.
 24. The display screen as in claim 1,further comprising: a Fresnel lens layer placed on one side of theprismatic layer that is opposite to the side where the fluorescent layeris located, the Fresnel lens layer directing the excitation light to theprismatic layer.
 25. A display screen, comprising: a plurality of screenlayers which are engaged to form a planar stack and comprise: afluorescent layer comprising a plurality of parallel fluorescent stripesand absorbing excitation light at an excitation wavelength to emitvisible light at a different and visible wavelength, a plurality ofparallel stripe dividers each located between two adjacent fluorescentstripes, each strip divider having side walls that are reflective andopaque to the emitted visible light to optically isolate two adjacentfluorescent stripes, and a dielectric layer in contact with the stripedividers and spaced from the fluorescent layer to define a gap betweenthe dielectric layer and each fluorescent stripe.
 26. The display screenas in claim 25, wherein: the gap is filled with air.
 27. The displayscreen as in claim 25, wherein: the screen layers further comprise: anentrance layer to receive the excitation light and located on one sideof the fluorescent screen that is opposite to the dielectric layer, anda filter layer on one side of the fluorescent layer where the dielectriclayer is located, and the filter layer blocks transmission of theexcitation light and transmits the visible light with an attenuationuniform over a spectral range of the visible light.
 28. The displayscreen as in claim 25, wherein: the screen layers further comprise: anentrance layer to receive the excitation light and located on one sideof the fluorescent screen that is opposite to the dielectric layer, aselective blocking layer that transmits the visible light and blocks theexcitation light, and a neutral density filter layer that attenuates thevisible light with an attenuation uniform over a spectral range of thevisible light; and the selective blocking layer and the neutral densityfilter layer are located at a side of the fluorescent layer that isopposite to the side where the entrance layer is located.
 29. Thedisplay screen as in claim 25, wherein: the screen layers furthercomprise: a filter layer comprising a plurality of parallel filterstripes each aligned to a respective fluorescent stripe along adirection perpendicular to the screen layers, each filter stripe of thefilter layer being located between the gap and a respective fluorescentstripe, and at least three adjacent filter stripes are respectively madeof a first filter material to transmit first visible light of a firstcolor while absorbing light of other colors including a second color anda third color, a second filter material to transmit second visible lightof the second color while absorbing light of other colors including thefirst and the third colors, and a third filter material to transmitthird visible light of the third color while absorbing light of theother colors including the first and the second colors.
 30. The displayscreen as in claim 29, wherein: each filter stripe is formed between twoadjacent stripe dividers and thus aligns with a correspondingfluorescent stripe between the two adjacent stripe dividers.
 31. Thedisplay screen as in claim 30, wherein: the stripe dividers comprise awhite paint that is optically reflective and opaque.
 32. The displayscreen as in claim 31, wherein: the white paint comprises a mixture ofTiO₂ or barium sulfate and a resin.
 33. The display screen as in claim30, wherein: each stripe divider comprises a reflective metal coating.34. The display screen as in claim 30, wherein: each stripe dividerabsorbs the excitation light and emits fluorescent light at a wavelengthdifferent from the excitation light and the visible light.
 35. Thedisplay screen as in claim 25, further comprising: a Fresnel lens layerplaced on one side of the dielectric layer that is opposite to the sidewhere the fluorescent layer is located, the Fresnel lens layer directingthe excitation light to the dielectric layer.
 36. A display screen,comprising: a screen substrate; a fluorescent layer formed over thescreen substrate and comprising a plurality of parallel fluorescentstripes, the fluorescent layer absorbing excitation light to emitvisible light, wherein the excitation light and the visible light are atdifferent wavelengths; a plurality of parallel stripe dividers eachlocated between two adjacent fluorescent stripes; a dichroic layerformed over the screen substrate to receive the excitation light,wherein the dichroic layer transmits the excitation light and reflectsthe visible light.
 37. The display screen as in claim 36, furthercomprising: a dielectric layer having a plurality of dielectric stripeseach placed between the dichroic layer and the fluorescent layer andbetween two adjacent stripe dividers.
 38. The display screen as in claim36, further comprising: a filter layer formed over the screen substrateand comprising a plurality of parallel filter stripes each formedbetween two adjacent stripe dividers to align with a correspondingfluorescent stripe between the two adjacent stripe dividers, and whereinthe fluorescent layer is located between the dichroic layer and thefilter layer, wherein at least three adjacent filter stripes arerespectively made of a first filter material to transmit first visiblelight of a first color while absorbing light of other colors including asecond color and a third color, a second filter material to transmitsecond visible light of the second color while absorbing light of othercolors including the first and the third colors, and a third filtermaterial to transmit third visible light of the third color whileabsorbing light of the other colors including the first and the secondcolors.
 39. The display screen as in claim 38, further comprising: adielectric layer having a plurality of dielectric stripes each placedbetween two adjacent stripe dividers and between the fluorescent layerand the filter layer.
 40. The display screen as in claim 36, wherein:the stripe dividers comprise a white paint that is optically reflective.41. The display screen as in claim 40, wherein: the white paintcomprises a mixture of TiO₂ or barium sulfate and a resin.
 42. Thedisplay screen as in claim 36, wherein: each stripe divider comprises areflective metal coating.
 43. The display screen as in claim 36,wherein: each stripe divider comprises a fluorescent material that emitsfluorescent light at a wavelength different from the excitation lightand the visible light.
 44. The display screen as in claim 36, furthercomprising: a second dichroic layer that transmits the visible light andreflects the excitation light, the second dichroic layer formed over thescreen substrate, wherein the fluorescent layer is between the dichroiclayer and the second dichroic layer.
 45. The display screen as in 44;further comprising: a dielectric layer in contact with the seconddichroic layer, wherein the second dichroic layer is between thefluorescent layer and the dielectric layer.
 46. A display screen,comprising: a fluorescent layer comprising a plurality of parallelfluorescent stripes, the fluorescent layer absorbing excitation light toemit visible light, wherein the excitation light and the visible lightare at different wavelengths; an entrance layer formed on a first sideof the fluorescent layer to receive the excitation light and to directthe excitation light to the fluorescent layer; and a filter layer formeda second side of the fluorescent layer opposing the first side, thefilter layer formed of a material that transmits the visible light withan attenuation uniform over a spectral range of the visible light. 47.The display screen as in claim 46, wherein: the filter layer furtherblocks transmission of the excitation light.
 48. The display screen asin claim 46, further comprising: a second filter layer formed a secondside of the fluorescent layer opposing the first side, the second filterlayer blocking transmission of the excitation light and transmitting thevisible light.
 49. The display screen as in claim 46, wherein: theentrance layer comprises a prismatic layer which includes a plurality ofprism elements.
 50. The display screen as in claim 46, wherein: theentrance layer comprises a dielectric layer with a flat surface toreceive the excitation light.
 51. A display screen, comprising: afluorescent layer that absorbs excitation light to emit visible light;and a first layer on a first side of the fluorescent layer operable totransmit the excitation light and to reflect the visible light, thefirst layer comprising a prismatic layer which comprises a plurality ofprism elements.
 52. The display screen as in claim 51, wherein: thefluorescent layer comprises parallel fluorescent stripes and stripedividers between the fluorescent stripes.
 53. The display screen as inclaim 52, wherein: each stripe divider emits invisible fluorescent lightunder excitation by the excitation light.
 54. A display screen,comprising: a fluorescent layer that absorbs excitation light to emitwhite light, and an array of color filters adjacent to the fluorescentlayer to receive the emitted white light and to filter the white lightto transmit colored light, each color filter transmitting a designatedcolor and absorbing light of other colors, each designated color for onecolor filter being different from a designated color transmitted by aneighboring color filter.
 55. The display screen as in claim 54, furthercomprising: a first layer on a first side of the fluorescent layer totransmit the excitation light to the fluorescent layer and to reflectthe visible light.
 56. The display screen as in claim 55, wherein: thefirst layer comprises a prismatic layer which comprises a plurality ofprism elements.
 57. A display screen, comprising: a plurality of screenlayers which are engaged to form a planar stack and comprise: afluorescent layer comprising a plurality of parallel fluorescent stripesand absorbing excitation light at an excitation wavelength to emitvisible light at a different and visible wavelength, a plurality ofparallel stripe dividers each located between two adjacent fluorescentstripes, each strip divider having side walls that are reflective andopaque to the emitted visible light to optically isolate two adjacentfluorescent stripes, and a dielectric layer in contact with thefluorescent stripes and the stripe dividers to couple the excitationlight into the fluorescent stripes, a filter layer comprising aplurality of parallel filter stripes each aligned to a correspondingfluorescent stripe along a direction perpendicular to the screen layers,the fluorescent layer being located between the high-index dielectriclayer and the filter layer, wherein at least three adjacent filterstripes are respectively made of a first filter material to transmitfirst visible light of a first color while absorbing light of othercolors including a second color and a third color, a second filtermaterial to transmit second visible light of the second color whileabsorbing light of other colors including the first and the thirdcolors, and a third filter material to transmit third visible light ofthe third color while absorbing light of the other colors including thefirst and the second colors, a second dielectric layer between thefluorescent layer and the filter layer; and a plurality of secondparallel stripe dividers each located between two adjacent filterstripes and in contact with the second dielectric layer.
 58. The displayscreen as in claim 57, wherein: second parallel stripe dividers separatethe transparent dielectric layer and the filter layer from each other bya gap.
 59. The display screen as in claim 58, wherein: the gap betweenthe filter layer and the transparent dielectric layer is filled withair.
 60. The display screen as in claim 57, wherein: a facet of eachsecond parallel stripe divider that faces away from the fluorescentlayer is optically absorbent.
 61. A display screen, comprising: a firstdielectric layer that transmits excitation light at an excitationwavelength; a fluorescent layer comprising a plurality of parallelfluorescent stripes and absorbing the excitation light to emit visiblelight at a different and visible wavelength; and a second dielectriclayer spaced from the fluorescent stripes by an air gap, wherein thesecond dielectric layer at least partially transmits the visible light,and wherein the fluorescent layer is positioned between the first andsecond dielectric layers.
 62. The display screen as in claim 61,wherein: the second dielectric layer blocks the excitation light. 63.The display screen as in claim 61, wherein: the second dielectric layeruniformly attenuates light in a visible spectral range.
 64. The displayscreen as in claim 61, wherein: the second dielectric layer blocks theexcitation light and uniformly attenuates light in a visible spectralrange.